The clustering fluid such as the HF gas and the like has been widely utilized in the fields of the production of chemicals, semiconductors and the like. Accordingly, a wide variety of flow rate control devices are used in the facilities to supply the clustering fluid such as the HF gas and the like. Among others, a mass flow controller, a pressure difference type flow rate control device and the like are the ones comparatively widely utilized.
The clustering fluid such as the HF gas and the like is known as a substance having peculiar properties such as high density, high specific heat ratio, high dependence of the molecular association on the temperature and pressure, high dependence of an endothermic amount on the temperature at the time of the molecular dissociation, and the like.
Therefore, Boyle's and Charles' law does not apply to the clustering fluid unlike ideal gases like the oxygen gas or the nitrogen gas, and in regard with the flow control there exist many problems which are not encountered when controlling the flow rate control of the oxygen gas or the nitrogen gas. This is because the molecular weight of the clustering fluid such as the HF gas and the like greatly changes depending on the pressure fluctuations and others due to dependence of the molecular association on the temperature and pressure, and even if the clustering fluid such as the HF gas and the like has the same weight, the number of mole of the clustering fluid changes when the molecular weight M changes.
Because the association heat of the molecules of the clustering fluid such as the HF gas and the like is great, the bigger the pressure difference is when it is supplied, the larger endothermic effects result. In the event that the endothermic effects are remarkable, a problem such as liquefaction will occur because of the low steam pressure.
Hence, with the conventional supply systems for the clustering fluid such as the HF gas and the like, it has been tried to improve precision of the flow rate control precision of the clustering fluid such as the HF gas and the like by mixing the clustering fluid in a large amount of the diluting gas and controlling the diluting gas so that a high precision flow rate control of the clustering fluid such as the HF gas and the like can be achieved. Or, a heating device is installed at the supply source of the clustering fluid such as the HF gas and the like so that the clustering fluid such as the HF gas and the like is supplied under a relatively high pressure and in a state in which the clustering of the fluid is made difficult by heating the fluid at a high temperature.